Role of dietary choices in the ability of bobwhite to discriminate between insecticide-treated and untreated food

Abstract

Tests were conducted to determine the dietary concentrations at which 14-d-old bobwhite (Colinus virginianus) chicks could discriminate between food treated (TRT) with two organophosphorus (OP) insecticides (chlorpyrifos and methyl parathion) and untreated (UNT) food. Results of subacute dietary LC50 tests using one feeder of TRT food per cage were compared with those of tests in which birds were presented with two feeders (one TRT and one UNT, 1:1) or 10 feeders (five TRT and five UNT, 5:5; or nine TRT and one UNT, 9:1). The dietary concentration above which birds discriminated between TRT and UNT feeders by consuming a greater proportion of UNT food was defined as the discrimination threshold (DT). The DT occurred at sublethal dietary concentrations in all chlorpyrifos tests (DT = 45 ppm in 1:1 test, 24 ppm in 5:5 test and 69 ppm in 9:1 test; LC50 = 647 ppm) but increased in the methyl parathion tests as the number of choices and the relative proportion of TRT feeders increased (DT = 10 ppm in 1:1 test, 46 ppm in 5:5 test and >126 ppm in 9:1 test; LC50 = 91 ppm). The different responses were probably due to differences in the intensity of sensory cues presented by the two chemicals as the chicks developed conditioned aversions to them. In all tests, mortality was inversely related to total food consumption. No relationship was found between mortality and the amount of active ingredient ingested per bird-day. Consequently, the ability to locate UNT feeders was more important than the amount of chemical ingested. When alternative food choices exist, vulnerability to poisoning can be influenced by the number and relative abundance of those choices, as well as a bird's ability to detect the chemical.